So how did crystal sets work? They're completely passive. The problem isn't that you can't transmit energy (what else is electromagnetic radiation?), more that the energy density might not be high enough for his application.

It's possible to light a torch bulb from a MW radio station, but only with a tuned loop antenna which has an effective size on the order of a wavelength irrespective of it's physical size.

A standard wifi hotspot does radiate enough power to light an LED dimly, but you will only capture the tiniest fraction of this. If you really need wireless power you will have to construct a separate source and you should expect the efficiency to be dismal

The total output of a wi-fi router might be 100mW. That's barely enough for an LED even if you could capture all of it, and of course you can only get a tiny fraction at any distance.

Not going to work. Look into a wi-fi sniffer. They're the size of a keychain fob and include a signal strength indication. But of course they contain a battery.

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this wifi sniffer is cool kind of stuff. i will make one of that. and i searched a good circuit about it.

and sir. can you suggest any good project study? i want a project study that is simple but will make a big impact. im thinking about home automation using android phone but they are releasing stuff and theyre good. now i have to think another. >.<